The possibility of preparing hybrid genes by gene technology has opened up new routes for the workup of recombinant proteins. By linking the coding gene sequence of a desired protein to the coding gene sequence of a protein fragment having a high affinity for a ligand (affinity peptide), it is possible to purify desired recombinant proteins in the form of fusion proteins in one step using the affinity peptide.
By site-directed mutagenesis it is also possible to introduce specific chemical or enzymatic cleavage sites at the point of linkage of the affinity peptide and the desired recombinant protein, so that after the purification of the fusion protein by means of a suitable affinity resin, the desired recombinant protein can be recovered by chemical or enzymatic cleavage. Such purification methods have been described, for example, in Science 198, 1056-1063 (1977) (Itakura et al.); Proc. Natl. Acad. Sci. U.S.A. 80, 6848-6852 (1983) (Germino et al.); Nucleic Acids Res. 13, 1151-1162 (1985) (Nilsson et al.): Gene 32, 321-327 (1984) (Smith et al.). and European Patent Applications publication Nos. 150 126 and 184 355.